The present invention concerns a method and apparatus for automatically verifying and loading precision drill bits into a drilling machine package. More particularly, it relates to an apparatus which transfers drill bits from pre-configured drill bit containers to a diameter verification station and then to ready-for-use, printed circuit board drilling machine packages.
The manufacture of printed circuit boards (PCBs) has experienced considerable improvement over the past 25 years. Technological advancements in chemistry, machinery, and materials have resulted in an ability to consistently produce large volumes of PCBs with dense circuitry patterns on a highly efficient basis.
One particular area of progress has been in the PCB drilling process. An individual circuit board has literally thousands of drilled holes. As normal fabrication techniques place several circuit boards on a panel for processing, a single panel can have tens of thousands of drilled holes. These holes are used to connect components to the board and to various circuitry traces, to connect the circuitry traces of one layer to another, to provide reference points for subsequent processing, and to assist in mounting the completed circuit board within its final housing.
Drill bits used in drilling PCBs are made of a strong, wear resistant material, such as tungsten carbide. While this material is resistant to wear, after a certain number of drilled holes ("hits"), the drill bit will deteriorate and will no longer be sharp enough to maintain the diameter and tolerance requirements for subsequent holes. Accounting for drill bit deterioration during processing is highly important as oftentimes, a particular panel requires hundreds of holes of the same diameter. Becuase of wear, single drill bits will be unable to drill all holes within tolerances. Through experience, circuit board manufacturers have approximated the rate at which drill bits dull. Thus, based upon this wearing rate, the drill bit is replaced after a certain number of hits.
The drilling requirements for jobs vary, but generally, differently sized (diameter) holes, and thus differently sized drill bits, are employed. Currently, approximately 255 standard sized drill bits are available, ranging from 0.002 inches to 0.2610 inches in diameter. A normal drilling job requires holes, and therefore drill bits, of several different diameters. Further, due to the known wear of drill bits, the tolerance specifications for the job will demand the use of a number of same diameter drill bits. Thus, during the course of a normal job, a drilling machine will be required to make a number of drill bit changes.
The first generation of drilling machines employed a single spindle device which was manually maneuvered by an operator to drill holes in a single circuit board. When job specifications called for the use of multiple drill bits, the operator was required to change drill bits by hand. Later, several spindle s were linked to one another so that more than one panel could be drilled at a time. Modern drilling machines employ multiple spindles and a movable work table to which the panels are secured. Via computer numerical control (CNC), the automated work table and attached panels are moved beneath the spindles for drilling the necessary holes.
Along with properly positioning panels for each drilled hole, the CNC drilling machine similarly automates the change of drill bits. For the CNC machine to replace drill bits on an automated basis, each individual drill bit must be stored on the work table at a pre-determined location, the coordinates of which are programmed into the drilling machine's memory.
During a drill bit change, the work table positions a new drill bit to be picked up directly below an associated spindle. To accomplish proper positioning, the drill bits for each job are grouped together on a cassette or package. For purposes of this specification, the terms "cassette" and "package" are used interchangeably, although a "package" is normally understood to mean a "cassette" that has been loaded with drill bits. The package has a plurality of drill bit receiving openings specifically arranged to maintain each individual drill bit at a standardized or known location. The drill bits are sequenced within the drilling package according to the hole diameters required by the PCB to be drilled. For example, a particular job may require the use of five drill bits of a first diameter, three drill bits of a second diameter and two drill bits of a third diameter. A drilling package having 10 consecutive drill bit openings would contain the first diameter drill bits in openings 1-5, the second diameter drill bits in openings 6-8, and the third diameter drill bits in openings 9-10. This sequence is programmed into the CNC drilling machine's memory so that when called for, the work table will precisely position the attached package beneath the spindle to deliver a drill bit of the desired diameter from the proper location in the package.
Configuration of drilling packages varies from manufacturer to manufacturer. A number of competing drilling machine manufacturers exist, such as Excellon Automation, DynaMotion, Hitachi, Posalux, and Advanced Controls. Each of these manufacturers have developed their own individual drilling package design. Each style of drilling package spaces the drill bit receiving openings differently and further employs unique row and column configurations for sequencing of drill bits. When a drilling machine retrieves a drill bit from a package, the computer-controlled movements are dictated by the assumed location of drill bits within the package attached to the work table. Thus, because of the variation in drilling package designs, a drilling machine for one manufacturer cannot properly function with another's drilling package as the drill bits will not be located in the position pre-programmed into the CNC drilling machine's memory.
While the drilling process itself has been automated, actual loading of drilling packages remains primarily a manual operation. As previously described, a machine-ready drilling package is comprised of a base cassette loaded with drill bits of specific diameters in a specific sequence according to job requirements. Manual loading of a drilling package requires an operator to first retrieve the proper manufacturer's drilling package based upon the type of drilling machine to be used. Next, an appropriate number of drill bits of each diameter required by the job must be selected. Prior to the loading process, drill bits are stored in a drill bit container. A drill bit container holds a number of drill bits of a same diameter, this diameter being plainly designated on the drill bit container itself. The operator manually transfers the required number of drill bits from each drill bit container and places them in the appropriate sequence within the drilling package.
The manual loading of drilling packages is a tedious process. Because the operator is required to make numerous decisions as he or she loads the drilling package on a repetitive basis, the opportunity for human error is quite prevalent. For example, drill bits of the wrong diameter may be erroneously selected and loaded. Similarly, an incorrect number of drill bits of a certain diameter might be placed in the package. Further complicating the manual loading of drilling packages is the fact that it is often quite difficult to visually detect an error in loading. Thus, mistakes in sequencing and/or drill bit diameter go unnoticed until the drilling process actually takes place. At this time, the results are usually quite damaging as a single hole or series of wrong diameter holes are drilled, severely damaging the circuit board(s) being operated on.
An additional problem with manual loading of drilling packages arises when drill bits of the wrong diameter have been placed within a drill bit container. When retrieving individual drill bits from a drill bit container, the operator assumes that the diameter designation is accurate for all drill bits contained therein. However, this is not always the case as drill bit containers can be mismarked. A similar problem occurs when re-sharpened drill bits are used. While the re-sharpened drill bits originally conformed in diameter to tolerances, the re-sharpening process may have dropped the drill bit out of tolerance. As time constraints do not allow the operator to verify the diameter of each drill bit being loaded, a mismarked or out of tolerance drill bit may erroneously be placed in a drilling package and go unnoticed until a PCB has been irreparably damaged.
A final concern associated with the manual loading of drilling packages is operator safety. Drill bit blades have sharp tips and, due to their inherently small diameters, are easily broken. These aspects present safety hazards to an operator as the drill bits are generally stored in both drill bit containers and drilling packages with the blade projecting outward. When reaching for an individual drill bit, it is quite common for the operator to contact other drill bit blades, causing painful cuts to the operator's fingers. Furthermore, the blade can break and become lodged in the finger, requiring medical attention for removal.
Manual loading of a drilling package with appropriately sized and sequenced drill bits is a labor intensive process, subject to numerous potential errors. Further, the inability to verify the diameter of each drill bit being loaded and operator safety presents additional concerns. Therefore, a substantial need exists for an automated drilling package loader, having the ability to verify the diameter of each drill bit being loaded along with accurately sequencing the drill bits within a variety of different manufacturer's drilling packages.